Forming a fin cut in a hardmask

ABSTRACT

A method of fabricating a hard mask structure is provided. According to the method, a hard mask layer is disposed over a substrate. The hard mask layer includes a lower hard mask layer disposed over the substrate and an upper hard mask layer disposed over the lower hard mask layer. The hard mask layer is patterned and the upper hard mask layer is removed by selectively etching the upper hard mask layer until reaching the lower hard mask layer to form a top portion of the hard mask structure having a first dimension. A spacer material is disposed on a sidewall of the top portion of the hard mask structure. The lower hard mask layer is removed by selectively etching the lower mask layer until reaching the substrate to form a bottom portion of the hard mask structure having a second dimension.

DOMESTIC PRIORITY

This application is a Continuation of Non-Provisional application Ser. No. 15/275,999, entitled “FORMING A FIN CUT IN A HARDMASK,” filed Sep. 26, 2016 which is incorporated herein by reference in its entirety.

BACKGROUND

The present invention generally relates to methods of fabricating a semiconductor device, and more particularly, to methods of fabricating the fin element of a fin-type field effect transistor (finFET). A known type of metal oxide semiconductor field effect transistors (MOSFET) is a non-planar device known generally as a fin-type field effect transistor (FinFET). The basic electrical layout and mode of operation of a FinFET device does not differ significantly from a traditional field effect transistor (FET). In contrast to a planar MOSFET, however, the source, drain and channel regions of a FinFET are built as a three-dimensional fin/bar on top of a local shallow trench isolation (STI) region and a semiconductor substrate. The gate electrode is wrapped over the top and sides of a middle portion of the fin such that the grate electrode is substantially perpendicular with respect to the fin. This middle portion of the fin, which is under the gate electrode, functions as the channel and provides an increased effective channel width compared to planar MOSFETs. The source and drain regions are the portions of the fin on either side of the channel that are not under the gate electrode. The source and drain regions can be suitably doped to produce the desired FET polarity, as is known in the art. The dimensions of the fin establish the effective channel length for the transistor.

SUMMARY

Embodiments detailing a method of fabricating a hard mask structure are provided. According to the method, a hard mask layer is disposed over a substrate. The hard mask layer includes a lower hard mask layer disposed over the substrate and an upper hard mask layer disposed over the lower hard mask layer. The hard mask layer is patterned and the upper hard mask layer is removed by selectively etching the upper hard mask layer until reaching the lower hard mask layer to form a top portion of the hard mask structure having a first dimension. A spacer material is disposed on a side wall of the top portion of the hard mask structure. The lower hard mask layer is removed by selectively etching the lower mask layer until reaching the substrate to form a bottom portion of the hard mask structure having a second dimension.

Other embodiments provide a method of fabricating a semiconductor device. According to the method, a plurality of the hard mask structures separated from each other by a plurality of trenches is formed. The trenches are filled out with the spacer material so as to form a protective layer, wherein only a top surface of the hard mask structures is exposed. A mask layer over the protective layer is disposed, wherein the mask layer has an opening over an unwanted hard mask structure. The unwanted hard mask structure, the mask layer, and the spacer material from the trenches are subsequently removed. A portion of the substrate is removed by selectively etching the exposed areas of the substrate to form a base of the hard mask structure.

Yet other embodiments provide a hard mask structure including a top portion having a first dimension, and a bottom portion disposed under the top portion and having a second dimension, wherein the second dimension is greater than the first dimension.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The forgoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a cross-sectional view of a conventional hard mask structure disposed over a substrate;

FIG. 2 is a cross-sectional view of the hard mask structure, according to an embodiment of the present invention;

FIG. 3 is a cross-sectional view of the hard mask layer disposed over the substrate, according to an embodiment of the present invention;

FIG. 4 is a cross-sectional view of the patterned hard mask, according to an embodiment of the present invention;

FIG. 5 illustrates a formation of the top portion of the hard mask structure having a first (smaller) dimension, according to an embodiment of the present invention;

FIG. 6 illustrates deposition of the dielectric spacer, according to an embodiment of the present invention;

FIG. 7 illustrates formation of the bottom portion of the hard mask structure having a second (larger) dimension, according to an embodiment of the present invention;

FIG. 8 illustrates formation of the protective layer by filling out the trenches between the hard mask structures with the spacer material, according to an embodiment of the present invention;

FIG. 9 illustrates deposition of the masking layer over the hard mask structures with an opening over the unwanted structure, according to an embodiment of the present invention;

FIG. 10 illustrates removal of the unwanted hard mask structure by selective etching, according to an embodiment of the present invention;

FIG. 11 illustrates a desired pattern of the hard mask structures disposed over the substrate, according to an embodiment of the present invention; and

FIG. 12 illustrates a desired pattern of semiconductor fins, according to an embodiment of the present invention.

Reference is made below to the above-described drawings, which are not drawn to scale for ease of understanding, wherein the same reference numbers used throughout different figures designate the same or similar components.

DETAILED DESCRIPTION

Various embodiments of the present invention are described herein with reference to the related drawings. Alternative embodiments can be devised without departing from the scope of this invention. It is noted that various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. As an example of an indirect positional relationship, references in the present description to forming layer “A” over layer “B” include situations in which one or more intermediate layers (e.g., layer “C”) is between layer “A” and layer “B” as long as the relevant characteristics and functionalities of layer “A” and layer “B” are not substantially changed by the intermediate layer(s).

The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as an example, instance or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms “at least one” and “one or more” are understood to include any integer number greater than or equal to one, i.e., one, two, three, four, etc. The terms “a plurality” are understood to include any integer number greater than or equal to two, i.e., two, three, four, five, etc. The term “connection” can include both an indirect “connection” and a direct “connection.”

For the sake of brevity, conventional techniques related to semiconductor device and IC fabrication may or may not be described in detail herein. Moreover, the various tasks and process steps described herein can be incorporated into a more comprehensive procedure or process having additional steps or functionality not described in detail herein. In particular, various steps in the manufacture of semiconductor devices and semiconductor-based ICs are well known and so, in the interest of brevity, many conventional steps will only be mentioned briefly herein or will be omitted entirely without providing the well-known process details.

By way of background, however, a more general description of the semiconductor device fabrication processes that can be utilized in implementing one or more embodiments of the present invention will now be provided. Although specific fabrication operations used in implementing one or more embodiments of the present invention can be individually known, the described combination of operations and/or resulting structures of the present invention are unique. Thus, the unique combination of the operations described in connection with the present invention utilize a variety of individually known physical and chemical processes performed on a semiconductor (e.g., silicon) substrate, some of which are described in the following immediately following paragraphs.

In general, the various processes used to form a micro-chip that will be packaged into an IC fall into four general categories, namely, film deposition, removal/etching, semiconductor doping, and patterning/lithography. Deposition is any process that grows, coats, or otherwise transfers a material onto the wafer. Available technologies include physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE), and more recently, atomic layer deposition (ALD) among others. Removal/etching is any process that removes material from the wafer. Examples include etch processes (either wet or dry), and chemical-mechanical planarization (CMP), and the like. Semiconductor doping is the modification of electrical properties by doping, for example, transistor sources and drains, generally by diffusion and/or by ion implantation. These doping processes are followed by furnace annealing or by rapid thermal annealing (RTA). Annealing serves to activate the implanted dopants. Films of both conductors (e.g., poly-silicon, aluminum, copper, etc.) and insulators (e.g., various forms of silicon dioxide, silicon nitride, etc.) are used to connect and isolate transistors and their components. Selective doping of various regions of the semiconductor substrate allows the conductivity of the substrate to be changed with the application of voltage. By creating structures of these various components, millions of transistors can be built and wired together to form the complex circuitry of a modern microelectronic device.

Fundamental to the above-described fabrication processes is semiconductor lithography, i.e., the formation of three-dimensional relief images or patterns on the semiconductor substrate for subsequent transfer of the pattern to the substrate. In semiconductor lithography, the patterns are a light sensitive polymer called a photo-resist. To build the complex structures that make up a transistor and the many wires that connect the millions of transistors of a circuit, lithography and etch pattern transfer steps are repeated multiple times. Each pattern being printed on the wafer is aligned to the previously formed patterns and slowly the conductors, insulators, and selectively doped regions are built up to form the final device.

Aspects of the present invention and certain features, advantages, and details thereof, are explained more fully below with reference to the non-limiting embodiments illustrated in the accompanying drawings. Descriptions of well-known materials, fabrication tools, processing techniques, etc., are omitted so as to not unnecessarily obscure the invention in detail. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the invention, are given by way of illustration only, and are not by way of limitation. Various substitutions, modifications, additions and/or arrangements within the spirit and/or scope of the underlying invention will be apparent to those skilled in the art from this description.

Turning now to a description of technologies that are more specifically relevant to embodiments of the present invention, Field effect transistors (FETs) are semiconductor devices fabricated on a bulk semiconductor substrate or on a silicon-on-insulator (SOI) substrate. FET devices generally consist of a source, a drain, a gate, and a channel between the source and drain. The gate is separated from the channel by a thin insulating layer, typically of silicon oxide, called the field or gate oxide. A voltage drop generated by the gate across the oxide layer induces a conducting channel between the source and drain thereby controlling the current flow between the source and the drain. Current integrated circuit designs use complementary metal-oxide-semiconductor (CMOS) technology that use complementary and symmetrical pairs of p-type and n-type metal oxide semiconductor field effect transistors (MOSFETs) for logic functions.

The integrated circuit industry is continually reducing the size of the devices, increasing the number of circuits that can be produced on a given substrate or chip. It is also desirable to increase the performance of these circuits, increase the speed, and reduce the power consumption. A three dimensional chip fabrication approach, such as a finFET, has been developed for semiconductor devices. A finFET is a non-planar FET. The “fin” is a narrow, vertical silicon based channel between the source and the drain. The fin is covered by the thin gate oxide and surrounded on two or three sides by an overlying gate structure. The multiple surfaces of the gate, allow for more effective suppression of “off-state” leakage current. The multiple surfaces of the gate also allow enhanced current in the “on” state, also known as drive current. These advantages translate to lower power consumption and enhanced device performance.

Process challenges exist as the dimensions of the devices decrease. Uniformity of the various layers of fabrication becomes more important as feature sizes are reduced, some now falling below 20 nm. Small variations in layer thickness have a larger impact on process variation and control. New process schemes are required to tolerate variations and maintain process control. Specifically, thick and stable fin hard masks are needed for Fin patterning, downstream chemical-mechanical polishing, and fin reveal.

Turning now to an overview of the present invention, one or more embodiments provide a method of fabricating a hard mask structure. According to the method, a hard mask layer is disposed over a substrate. The hard mask layer includes a lower hard mask layer disposed over the substrate and an upper hard mask layer disposed over the lower hard mask layer. The hard mask layer is patterned and the upper hard mask layer is removed by selectively etching the upper hard mask layer until reaching the lower hard mask layer to form a top portion of the hard mask structure having a first dimension. A spacer material is disposed on a side wall of the top portion of the hard mask structure. The lower hard mask layer is removed by selectively etching the lower mask layer until reaching the substrate to form a bottom portion of the hard mask structure having a second dimension.

Other embodiments provide a method of fabricating a semiconductor device. According to the method, a plurality of the hard mask structures separated from each other by a plurality of trenches is formed. The trenches are filled out with the spacer material so as to form a protective layer, wherein only a top surface of the hard mask structures is exposed. A mask layer over the protective layer is disposed, wherein the mask layer has an opening over an unwanted hard mask structure. The unwanted hard mask structure, the mask layer, and the spacer material from the trenches are subsequently removed. A portion of the substrate is removed by selectively etching the exposed areas of the substrate to form a base of the hard mask structure.

Yet other embodiments provide a hard mask structure including a top portion having a first dimension, and a bottom portion disposed under the top portion and having a second dimension, wherein the second dimension is greater than the first dimension.

The phrase “dimension” and variations thereof are used herein to identify dimensions of semiconductor device features that can impact the performance of the device (e.g., increase parasitic capacitance, etc.). Dimensions are often adjusted using a variety of means in order to optimize device performance and yield in manufacturing. The semiconductor features that are considered dimensions depend on a variety of factors, including, for example, the specifics of the relevant process technologies.

FIG. 1 shows a typical current hard mask disposed on a substrate 101, wherein individual structures 102 have uniform dimensions. It was found, however, that such a hard mask does not show good stability. As previously noted, thick and stable fin hard masks are needed for Fin patterning, downstream chemical-mechanical polishing, and fin reveal. The inventors of the present application unexpectedly found that hard mask structures having two dimensions have improved stability and can be reliably used in a FinFET process.

FIG. 2 shows a hard mask structure 103, according to an embodiment of the present invention. The hard mask structure 103 is disposed on the substrate 101, which includes a top portion 104 having a first dimension, which in some embodiments can be a dimension, and a bottom portion 105 disposed under the top portion 104 and having a second dimension, which in some embodiments can be a dimension. In some embodiments, the second dimension is greater than the first dimension. In one or more embodiments, the first and/or second dimensions are a width of the corresponding portion of the hard mask structure measured from the point on the left hand side to the point on the right hand side of the structure.

Another embodiment provides a method of forming a hard mask structure. FIG. 3 illustrates a hard mask layer 106 disposed over the substrate 101. The hard mask layer 106 is used to define the substrate during the substrate etch process and can also protect the substrate during subsequent processing steps. For illustrative purposes, the thickness variations that can be present in the substrate 101 and the hard mask layer 106 have been exaggerated. In an embodiment, the hard mask layer 106 can include two layers: a first hard mask layer 107, deposited over the substrate 101 and a second hard mask layer 108, deposited over the first hard mask layer 107. The first hard mask layer 107 and the second hard mask layer 108 may include the same or different materials. In an embodiment, the first hard mask layer (or lower hard mask layer) 107, deposited over the substrate 101 can be manufactured of silicon nitride (SiN), deposited using, for example, low pressure chemical vapor deposition (LPCVD). In other embodiments, the first hard mask layer 107 materials can include, but are not limited to, hafnium oxide (HfO₂) or tantalum nitride (TaN). The first hard mask layer 107 disposed over the substrate 101 is a layer of sufficient thickness to protect the substrate 101 from damage during the removal of subsequent layers. It is also desirable to keep the first hard mask layer 107 sufficiently thin thereby reducing thickness variability and reducing the etch time required for subsequent removal, as will be discussed below. In an embodiment, the first hard mask layer 107 is about 10 nanometers to about 50 nanometers thick, for example, about 10 nanometers to about 30 nanometers thick, or about 30 nanometers thick, and is conformal to the top surface of the substrate 101.

The second hard mask layer 108 is deposited over the first hard mask layer 107. In an embodiment, the second hard mask layer (or upper hard mask layer) 108 can be the same material as the first hard mask layer 107, preferably SiN, deposited using, for example, LPCVD. Other second hard mask layer 108 materials can include, but are not limited to, hafnium oxide (HfO₂) or tantalum nitride (TaN). The second hard mask layer 108 can be of a sufficient thickness to protect the first hard mask layer 107 and the substrate 101 during subsequent processing steps described below. In an embodiment, the second hard mask layer 108 is about 10 nanometers to about 50 nanometers thick, for example, about 10 nanometers to about 30 nanometers thick, or about 30 nanometers thick. A person of ordinary skill in the art will recognize that chemical-mechanical planarization (CMP) steps can be inserted after the dielectric deposition processes to further planarize the surface. It should also be recognized that thickness variability caused by the CMP process will occur only in the second hard mask layer 108, and not in the first hard mask layer 107.

As shown in FIG. 4, the hard mask layer 106 can then be patterned to provide an etch mask 109. The patterning can be performed by Extreme Ultraviolet Lithography (EUV), Self-Aligned Double Patterning (SADP), or Self-Aligned Quadruple Patterning (SAQP). In an embodiment, standard photolithographic processes can be used to define the pattern of the etch mask 109 deposited over the second hard mask layer 108. The same pattern can then be formed in the second hard mask layer 108 by removing the second hard mask layer 108 from the areas not protected by the pattern.

The second hard mask layer 108 can be removed using, for example, an isotropic etching. In an embodiment, reactive ion etching (RIE) can be used to remove the second hard mask layer 108. This removal provides a top portion 104 of the hard mask structures 103 having the first dimension (FIG. 5). RIE uses chemically reactive plasma, generated by an electromagnetic field, to remove various materials. In an embodiment, the first dimension of the top portion of the hard mask structure may be from about 4 nanometers to about 8 nanometers. A person of ordinary skill in the art will recognize that the type of plasma used will depend on the material of which second hard mask layer 108 is composed, or that other etch processes, e.g., wet chemical etch, laser ablation, etc., can be used.

As shown in FIG. 6, a dielectric spacer 110 can be disposed over a sidewall of the top portion 104 of the hard mask structure 103 and over a sidewall of the etch mask 109 in order to enlarge the second dimension of the bottom portion 105 of the hard mask structure 103. The dielectric spacer can be any non-metal oxide spacer known in the art. For example, forming dielectric spacer 110 can include depositing a conformal layer (not shown) of insulating material, such as silicon nitride, over the sidewall of the top portion 104 of the hard mask structure 103 and over the sidewall of the etch mask 109. An anisotropic etch process, wherein the etch rate in the downward direction is greater than the etch rate in the lateral direction, can be used to remove the insulating layer, thereby forming dielectric spacer 110. The etch process can be controlled such that the insulating layer can be removed from the sidewall of the top portion 104 of the hard mask structure 103 and over the sidewall of the etch mask 109 while forming dielectric spacer 110.

The unmasked portion of the first hard mask layer 107 can then be selectively etched as defined by the position of the dielectric spacer 110 to provide the bottom portion 105 of the hard mask structure 103 having the second dimension. The removal of the first hard mask layer 107 can be performed by isotropic etching. In an embodiment, reactive ion etching (RIE) can be used to remove the first hard mask layer 107. RIE uses chemically reactive plasma, generated by an electromagnetic field, to remove various materials. In an embodiment, the second dimension of the bottom portion of the hard mask structure may be from about 8 nanometers to about 20 nanometers. A person of ordinary skill in the art will recognize that the type of plasma used will depend on the material of which first hard mask layer 107 is composed, or other etch processes, e.g., wet chemical etch, laser ablation, etc., can be used. During the process, the etch mask 109 can also be removed. As a result, a plurality of hard mask structures separated from each other by a plurality of trenches can be formed (FIG. 7).

The trenches can then be filled out with the spacer material 111 so as to form a protective layer, wherein only a top surface of the hard mask structures 103 is exposed. In an embodiment, the spacer material 111 can be the same as or different from the dielectric spacer 110 material (FIG. 8). A masking layer 112 can be disposed over the protective layer with an opening 113 over an unwanted hard mask structure 114 (FIG. 9). The unwanted hard mask structure 114 can be subsequently removed by dry or wet etching to leave a gap (void) 115 (FIG. 10).

The masking layer 112 and the spacer material 111 can then be removed to provide a desired pattern of the hard mask structures 103 (FIG. 11). Subsequent etching of the substrate will furnish the desired fins 116 (FIG. 12) disposed on a bottom portion 117 of the substrate 101 (FIG. 13).

Although the invention has been shown and described with respect to certain embodiments, certain equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, devices, circuits, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component which performs the specified function of the described component (i.e., that is functionally equivalent), even though not structurally equivalent to the described structure which performs the function in the herein illustrated exemplary embodiments of the invention. In addition, to the extent that a particular feature of the invention was described with respect to only one of several embodiments, such feature can be combined with one or more features of the other embodiments as desired for any given or particular application.

As used herein, the articles “a” and “an” preceding an element or component are intended to be nonrestrictive regarding the number of instances (i.e., occurrences) of the element or component. Therefore, “a” or “an” should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular.

As used herein, the terms “invention” or “present invention” are non-limiting terms and not intended to refer to any single aspect of the particular invention but encompass all possible aspects as described in the specification and the claims.

As used herein, the term “about” modifying the quantity of an ingredient, component, or reactant of the invention employed refers to variation in the numerical quantity that can occur, for example, through typical measuring and liquid handling procedures used for making concentrates or solutions. Furthermore, variations can occur from inadvertent error in measuring procedures, differences in the manufacture, source, or purity of the ingredients employed to make the compositions or carry out the methods, and the like. In one aspect, the term “about” means within 10% of the reported numerical value. In another aspect, the term “about” means within 5% of the reported numerical value. Yet, in another aspect, the term “about” means within 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1% of the reported numerical value.

It will also be understood that when an element, such as a layer, region, or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements can also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there are no intervening elements present, and the element is in contact with another element.

It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements can be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 

What is claimed is:
 1. A method of fabricating features of a semiconductor device, the method comprising: disposing a hard mask layer over a substrate, wherein the hard mask layer comprises a lower hard mask layer disposed over the substrate and an upper hard mask layer disposed over the lower hard mask layer; patterning the hard mask layer with an etch mask; removing the upper hard mask layer by selectively etching the upper hard mask layer until reaching the lower hard mask layer to form a top portion of the hard mask structure having a first dimension; disposing a spacer material on a sidewall of the top portion of the hard mask structure and over a sidewall of the etch mask; and removing the etch mask and the lower hard mask layer by selectively etching the lower mask layer until reaching the substrate to form a bottom portion of the hard mask structure having a second dimension.
 2. The method according to claim 1, wherein the second dimension of the bottom portion of the hard mask layer is greater than the first dimension of the top portion thereof.
 3. The method according to claim 1, wherein the spacer material is disposed on both sides of the top portion of the hard mask structure to predetermine the second dimension of the bottom portion thereof.
 4. The method according to claim 3, wherein the second dimension of the bottom portion of the hard mask structure is equal to a combined thickness of the spacer material disposed on both sides of the top portion of the hard mask and the first dimension of the top portion thereof.
 5. The method according to claim 1, wherein a thickness of the upper hard mask layer is from about 10 nanometers to about 30 nanometers.
 6. The method according to claim 1, wherein a thickness of the lower hard mask layer is from about 10 nanometers to about 30 nanometers.
 7. The method according to claim 1, wherein the first dimension of the top portion of the hard mask structure is from about 4 nanometers to about 8 nanometers.
 8. The method according to claim 1, wherein the second dimension of the bottom portion of the hard mask structure is from about 8 nanometers to about 20 nanometers.
 9. The method according to claim 1, wherein the substrate comprises silicon, germanium, or a combination thereof.
 10. The method according to claim 1, wherein the hard mask layer comprises silicon nitride.
 11. The method according to claim 1, wherein the spacer material comprises a non-metal oxide.
 12. The method according to claim 1, wherein the removal of the upper hard mask layer and the lower hard mask layer is performed by isotropic etching.
 13. The method according to claim 1, wherein the patterning is performed by extreme ultraviolet lithography, self-aligned double patterning, or self-aligned quadruple patterning.
 14. A semiconductor device comprising: hard mask structures comprising: a top portion having a first dimension; and a bottom portion disposed under the top portion and having a second dimension, the second dimension being greater than the first dimension; and spacer material filling trenches separating the hard mask structures from each other.
 15. The device of claim 14, further comprising: a substrate base disposed under the bottom portion of the hard mask structure.
 16. The device according to claim 15, wherein a third dimension of the substrate base is substantially equal to the second dimension of the bottom portion of the hard mask structure.
 17. The semiconductor structure according to claim 15, further comprising a substrate disposed under the substrate base.
 18. A semiconductor device comprising: hard mask structures comprising: a top portion having a first dimension; and a bottom portion disposed under the top portion and having a second dimension, the second dimension being greater than the first dimension; and a substrate base disposed under the bottom portion of the hard mask structure.
 19. The device according to claim 18, wherein a third dimension of the substrate base is substantially equal to the second dimension of the bottom portion of the hard mask structure.
 20. The semiconductor structure according to claim 18, further comprising a substrate disposed under the substrate base. 